The thing about popular music today is that most of it is the same regurgitated content designed to be successful and popular. Every now and then you get rare artists like Daft Punk or Lorde, etc who really bring creativity and originality to the scene, but more often than not you have songs designed to make money.
By popular music you shouldn't understand POP music, but music that is popular. Looking at popular music of the 20th century and now, has popular music gotten worse? If yes, why? Is it bad for society or it doesn't really matter?
I believe that, although the themes of popular music have not changed in decades - sex and power being prevalent themes throughout - , the expression of these themes has changed so that modern popular music is more simple than in past years. For instance, modern musicians tend to veil their references to sex more and more thinly, leaving little to their audience's imagination or their ability to interpret: Consider the explicit, bare line "pussy put his ass to sleep, now he calling me Nyquil" from Nicki Minaj's "Anaconda" as opposed to the titular innuendo in AC/DC's "You Shook Me All Night Long," which is itself thinly-veiled compared to the line "Don't keep me waiting when I'm in the mood," from Glenn Miller and The Andrew Sisters' "In the Mood," which hides its sexual undertones with discussion of dancing. For this reason, that modern artists expect less from their audiences and thus produce a simpler product which in turn (I believe) simplifies society, I believe that popular music is worse nowadays than it was before.
I answer yes, but only because of one factor: The way that popular music has become limited due to marketing and algorithms to generate specific sounds, the way that it's over-produced. We undoubtedly have more talented people producing records. The 21st century saw Americans listening to a Korean dance number. While I don't know if we have a band like The Beatles that are extremely popular while also exploring deep issues, those kinds of bands are inherently rare. There are tons of talented performers out there. I just lament more organic, creative, diverse music choices.
The old music we kept and still listen to is usually the best that was made. We have almost no idea what was the low-level popular music like in the 60's or 70's. I personally think in every domain (not only music) most of what people produce is superficial and bad and only a minority is truly good and inspiring. It is however true that nowadays, more and more people can pretend they're making music because they have access to cheap software and hardware.